The goal of this research is to develop new procedures which use carbon-carbon double bonds as activating groups for carbon-carbon bond forming reactions and to use these reactions for the synthesis of biologically active natural products. Lewis acid catalyzed Ene, Prins and Friedel-Crafts reactions will be explored and developed into generally useful synthetic methods. The use of alkylaluminum halides as Lewis acids will be explored. We have already established that these reagents are superior catalysts since they are also proton scavengers. The total synthesis of the cholesterol lowering agents compactin and mevinolin, the anbti-tumor agent podophyllotoxin, 17-keto steroids, kanokonal, cryptomeridiol and calameone and iso-calamenidol will be carried out. Compacting and mevionlin are the two members of the most promising class of cholesterol lowering agents. Podophylotoxin and related compounds are clinically useful in the treatment of cancer. The proposed route to 17-keto steroids is very short and is potentially applicable to industrial synthesis of steroids.